1. Field of the Invention
The present invention relates to a battery charging apparatus and in particular to a battery charging apparatus that provides a smooth transition between two different charging modes.
2. Description of Related Art
Currently, the increasing demand for higher performance power supply circuits has resulted in a continued development of voltage regulator devices. Many low voltage applications, such as for use in cell phones, pagers, laptops, camera recorders and other mobile battery operated devices, require the use of low drop-out (LDO) voltage regulators.
The LDO voltage regulators generally can provide a well-specified and stable DC voltage whose input to output voltage difference is low. The LDO voltage regulators are usually configured for providing the power requirements to electrical circuits. The LDO voltage regulators typically have an error amplifier, and a pass device, e.g., a power transistor. These two components are coupled in series. The error amplifier is coupled to an input terminal of the LDO voltage regulators, and the pass device is coupled to an output terminal of the LDO voltage regulators. The pass device can then drive an external load. However, the LDO voltage regulator loses its efficiency when the voltage of the battery that is being charged increases and the difference between the input-output voltages at the LDO voltage regulator drops.
Another regulator commonly used to provide DC current to electronic devices is boost regulator. It is a class of switching-mode power supply containing at least two semiconductor switches and at least one energy storage element. The boost regulator is capable of delivering an output DC voltage greater than its input DC voltage and it is particularly useful for battery charging operation when the voltage of the battery that is being charged is higher.
It would be desirable to have a battery charging device that combines the quality of a LDO voltage regulator and a boost regulator and capable of delivering an output voltage that is higher than the input voltage at the same time smoothly switches operation between these two types of regulators.